Olivine-based cathode active material for lithium secondary batteries and method for producing the same

Abstract

The olivine-based positive electrode active material for lithium secondary batteries according to the present invention comprises rod-shaped particles having an average length of the long side in the range of 250 nm to 350 nm and a short side length of 70 nm to 95 nm; and flake-shaped particles having an average length of the long axis of the wide surface in the range of 350 nm to 450 nm and a short axis length of 200 nm to 250 nm; wherein the quantity percentage of flake-shaped particles relative to the rod-shaped particles is in the range of 10% to 50%.

Description

[Technical Field]

[0001] The present invention relates to an olivine-based cathode active material for lithium secondary batteries and a method for producing the same. [Background technology]

[0002] As the electric vehicle market truly takes off, the market for positive electrode active materials, which account for more than 40% of the cost of lithium-ion batteries, is also growing rapidly every year. Automobiles are classified into six segments based on their overall length, from segment A for vehicles under 3,500 mm to segment F for vehicles over 5,000 mm. Accordingly, even in the case of electric vehicles using batteries, different positive electrode active materials are used to match the vehicle's class and driving range.

[0003] For electric vehicles with a driving range of 600 km or more on a single charge, high-energy-density lithium-ion batteries are required, necessitating the use of high-nickel NCM-based cathode active materials. For vehicles with a range of around 400 km, mid-ni NCM-based materials are used. However, for electric vehicles that do not require a high driving range and are relatively inexpensive, using materials that do not have high energy density but are highly safe and have a long lifespan is advantageous from a cost perspective.

[0004] Lithium iron phosphate cathode active material is an olivine-based structure composed of FeO6 octahedral sites and PO4 tetrahedral sites, and is a material in which lithium ions are desorbed and inserted through a one-dimensional pathway. This material has a price advantage because its main composition is Li, Fe, and P, and it is cheaper than NCA and NCM materials which mainly use Ni and Co, due to the lower cost of the metal minerals. Furthermore, its structure is stable due to strong PO bonding, and it has excellent thermal stability as there is no oxygen dissociation at high temperatures during charging. In addition, it has excellent lifespan characteristics, and there is a history of many electric vehicles using this material being produced in China.

[0005] However, since lithium ions are desorbed and inserted via one-dimensional diffusion, the primary particles must be manufactured to nano-size, and because the material itself does not have electrical conductivity, a uniform carbon coating must always be applied to the surface, which is a disadvantage. Nevertheless, in recent years, with the emphasis on high safety in electric vehicles, cell-to-pack and even cell-to-chassis technologies have been seriously developed, and the energy density difference compared to existing NCM systems is narrowing more and more.

[0006] Known methods for producing the lithium iron phosphate cathode active material include solid-phase methods, hydrothermal synthesis methods, and liquid-phase methods such as the supercritical water method. Recently, a glycothermal method has been developed that uses a non-reactive solution such as ethylene glycol or diethylene glycol as the reaction solvent. In the case of the hydrothermal synthesis method and the supercritical water method, the reaction takes place at high temperature / high pressure during the production of lithium iron phosphate nanopowder, which raises safety concerns. Furthermore, it is difficult to control the size and particle size distribution of the lithium iron phosphate nanopowder silver particles produced by the glycothermal method.

[0007] Therefore, there is a real need to develop a method for economically and efficiently producing lithium iron phosphate (LFP) cathode active materials with excellent energy density and electrochemical performance without process problems. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to provide an olivine-based cathode active material for lithium secondary batteries with improved energy density.

[0009] Furthermore, the present invention aims to provide a method for producing an olivine-based cathode active material for lithium secondary batteries with improved energy density. [Means for solving the problem]

[0010] An olivine-based positive electrode active material for a lithium secondary battery according to one embodiment of the present invention may include rod-shaped particles having an average length of 250 nm to 350 nm on the long side and an average length of 70 nm to 100 nm on the short side; and flake-shaped particles having an average length of 200 nm to 450 nm on the long axis of the broad surface and an average length of 100 nm to 250 nm on the short axis.

[0011] The rod-shaped particles may have rounded ends along the length of their longer sides, and the flake-shaped particles may have a shape in which the length of their shorter sides gradually decreases from the center of their longer sides toward the ends on both sides.

[0012] The number percentage of flake-shaped particles relative to the total number of rod-shaped and flake-shaped particles may be in the range of 1% to 50%.

[0013] The ratio of the length of the long side to the length of the short side of the rod-shaped particle may be in the range of 1.5 to 8.0, and the aspect ratio of the wide surface of the flake-shaped particle may be in the range of 1.0 to 3.0.

[0014] The chemical composition of the rod-shaped particles and flake-shaped particles may be represented by the following chemical formula 1.

[0015] [Chemical formula 1] Li x (Fe y M 1-y )PO4

[0016] Here, 0.99 ≤ x ≤ 1.03, 0.2 ≤ y ≤ 0.6, and M is one or more elements selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga.

[0017] The specific surface area of ​​the olivine-based cathode active material for the lithium secondary battery is 10 m². 2 / g or 30m 2 The range / g is also acceptable.

[0018] The olivine-based cathode active material for the lithium secondary battery may include a carbon coating layer located on the outer surface, and the mass percentage of carbon with respect to the total mass of the olivine-based cathode active material for the lithium secondary battery may be in the range of 1 wt% to 2 wt%.

[0019] Also, the carbon coating layer may be located in the range of 90% to 100% of the total surface area of the olivine-based cathode active material for the lithium secondary battery.

[0020] A method for manufacturing an olivine-based cathode active material for a lithium secondary battery according to another embodiment of the present invention includes steps of preparing a first reaction solution in which an iron raw material substance, a phosphorus raw material substance, and a doping raw material substance are dissolved in water, a second reaction solution in which a lithium raw material substance is dissolved in water, and an organic solvent in which a dispersant is dissolved; obtaining an organic solution by stirring while introducing the first reaction solution and the second reaction solution into a reactor containing the organic solvent in which the dispersant is dissolved; performing a reaction under normal pressure conditions where the reactor is not sealed while heating the reactor to maintain an internal temperature at 160°C to 180°C to obtain a precipitate; and firing the precipitate in a reducing atmosphere after separation and drying to obtain an olivine-based cathode active material.

[0021] The step of performing a reaction under normal pressure conditions where the reactor is not sealed while heating the reactor to maintain an internal temperature at 160°C to 180°C to obtain a precipitate may be performed by a reflux process.

[0022] In the step of preparing the organic solvent in which the dispersant is dissolved, the organic solvent may have a boiling point in the range of 150°C to 200°C.

[0023] In the step of preparing the organic solvent in which the dispersant is dissolved, the organic solvent may be one or more selected from dimethyl sulfoxide (DMSO), diglyme, triglyme, and dimethylformamide (DMF).

[0024] In the step of preparing the organic solvent in which the dispersant is dissolved, the dispersant may be one or more selected from polyvinylpyrrolidone (PVP), polyvinylphenol (PVPh), polyvinyl alcohol (PVA), polyvinylsulfonic acid, polyvinylsulfate metal salt, polyvinylcarboxylic acid, polyvinylcarboxylate metal salt, polyvinylpyridine (PVPy), copolymers thereof, cyclodextrin, dextran, polysaccharide or polyacrylic acid (PAA).

[0025] The step of preparing the organic solvent in which the dispersant is dissolved may include the step of stirring and dissolving the organic solvent and the dispersant charged into the reactor; the step of heating the organic solvent in which the dispersant is dissolved to a temperature of 50°C to 80°C.

[0026] The step of heating the organic solvent in which the dispersant is dissolved to a temperature in the range of 50°C to 80°C may be heating by continuously introducing an inert gas into the reactor.

[0027] In the step of preparing the organic solvent in which the dispersant is dissolved, the mass percentage of the dispersant with respect to the mass of the organic solvent may be 0.2 wt% to 2 wt%.

[0028] In the step of obtaining an organic solution by stirring while introducing the first reaction solution and the second reaction solution into the reactor containing the organic solvent in which the dispersant is dissolved, the molar ratio value of lithium element to the total molar number of iron element and doping element in the obtained organic solution may be 1.00 to 1.02.

[0029] The step of obtaining an organic solution by stirring while introducing the first reaction solution and the second reaction solution into the reactor containing the organic solvent in which the dispersant is dissolved includes introducing the first reaction solution and the second reaction solution into the reactor at a predetermined rate respectively, and the pH value of the organic solution in the reactor can be maintained constant, specifically, it can be maintained at 6.0 to 7.0.

[0030] The step of heating the reactor to a temperature in the range of 160°C to 180°C and performing a reflux reaction under atmospheric pressure conditions with the reactor not sealed to obtain a precipitate may be carried out for 3 to 24 hours.

[0031] The step of separating and drying the precipitate and then calcining it in a reducing atmosphere to obtain an olivine-based cathode active material may further include the step of separating and drying the precipitate and then mixing and milling it with a carbon coating raw material to obtain a mixture, and the step of calcining the obtained mixture in a reducing atmosphere may also be performed.

[0032] In the step of separating and drying the precipitate and then mixing and milling it with the carbon coating raw material to obtain a mixture, the mass percentage of the carbon coating raw material relative to the mass of the dried precipitate may be 5 wt% to 15 wt%.

[0033] The step of separating and drying the precipitate and then calcining it in a reducing atmosphere to obtain an olivine-based cathode active material may be performed by calcining at a temperature of 400°C to 700°C for 1 hour or more in a reducing atmosphere.

[0034] In the step of preparing a first reaction solution by dissolving an iron raw material, a phosphorus raw material, and a doping raw material in the water, the doping raw material may be a raw material containing one or more selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga. [Effects of the Invention]

[0035] The olivine-based cathode active material for lithium secondary batteries according to the present invention has the advantage of having excellent electrical conductivity as well as high energy density.

[0036] Furthermore, the method for producing an olivine-based cathode active material for lithium secondary batteries according to the present invention has the advantage of being able to produce an olivine-based cathode active material that has excellent electrical conductivity and high energy density. [Brief explanation of the drawing]

[0037] [Figure 1] Figure 1 shows SME analysis images of LFMP produced according to Examples 1 to 3. [Figure 2] Figure 2 shows SME analysis images of LFMP produced according to Comparative Examples 2 to 4. [Figure 3] Figure 3 shows the XRD analysis results of LFMP produced according to Example 2 and Example 3. [Figure 4] Figure 4 shows the XRD analysis results of LFMP produced according to Example 2 and Comparative Example 4. [Figure 5] Figure 5 shows the XRD analysis results of LFMP produced according to Comparison 2. [Modes for carrying out the invention]

[0038] Embodiments of the present invention will be described in detail below. However, these are presented as examples only and do not limit the present invention, which is defined solely by the scope of the claims described later.

[0039] In this invention, when we say that one member is located "on" another member, this includes not only cases where one member is in direct contact with another member, but also cases where another member is interposed between the two members.

[0040] In this invention, when a part is said to "include" a certain component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0041] <Olivine-based cathode active material for lithium secondary batteries> One embodiment of the present invention relates to an olivine-based cathode active material represented by the following chemical formula 1.

[0042] [Chemical formula 1] Lix (Fe y M 1-y )PO4

[0043] In the above chemical formula 1, Here, 0.99 ≤ x ≤ 1.03 and 0.2 ≤ y ≤ 0.6, and M is one or more elements selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga.

[0044] The olivine-based positive electrode active material for lithium secondary batteries according to the present invention can consist of particles of one or more shapes selected from rod-shaped or flake-shaped.

[0045] The average length of the long side of the rod-shaped particles may be 150 nm to 500 nm, and more specifically, 250 nm to 350 nm. The average length of the short side of the rod-shaped particles may be 60 nm to 120 nm, and more specifically, 70 nm to 100 nm.

[0046] On the other hand, the long side length of the rod-shaped particle refers to the length of the longer side in the longitudinal direction of a single rod-shaped particle, and the short side length refers to the length of the longer side in the width direction perpendicular to the long side. The ratio of the long side length to the short side length of the rod-shaped particle may be in the range of 1.5 to 8.0.

[0047] The rod-shaped particles may have rounded ends along their longer side.

[0048] The flake-like particles may have an average length of the major axis of their broad surface of 200 nm to 650 nm, specifically 350 nm to 450 nm. The flake-like particles may have an average length of the minor axis of their broad surface of 150 nm to 350 nm, specifically 200 nm to 250 nm.

[0049] On the other hand, the aspect ratio of the flake-shaped particles may be in the range of 1.0 to 3.0.

[0050] In addition, in the flake-shaped particles, the length of the minor axis may gradually decrease in the direction from the center of the major axis to both end portions.

[0051] On the other hand, the percentage of the number of flake-shaped particles with respect to the total number of the rod-shaped particles and the flake-shaped particles may be in the range of 1% to 50%, specifically, it may be in the range of 1% to 30%, and more specifically, it may be in the range of 1% to 10%.

[0052] When the olivine-based positive electrode active material for a lithium secondary battery is mixed with the rod-shaped particles and the flake-shaped particles in the above size range and quantity range, there is an advantage that the energy density and the battery capacity of the battery to which this is applied are improved.

[0053] The specific surface area of the olivine-based positive electrode active material for a lithium secondary battery according to the present invention may be in the range of 10 m 2 / g to 30 m 2 / g.

[0054] The specific surface area was measured using the Brunauer-Emmett-Teller Analysis method according to the nitrogen adsorption method, and nitrogen gas was adsorbed and desorbed on the surface of the solid material using the BET formula, and the specific surface area of the material was measured by measuring the adsorption amount for each partial pressure.

[0055] In addition, the olivine-based positive electrode active material for a lithium secondary battery according to the present invention may include a carbon coating layer located on the outer surface, and may be located in an area ranging from 90% to 100% of the total surface area of the olivine-based positive electrode active material particles for a lithium secondary battery. The mass percentage of carbon with respect to the total mass of the olivine-based positive electrode active material for a lithium secondary battery may be 1 wt% to 2 wt%.

[0056] When the carbon coating layer is contained within the specified range, it exhibits excellent electrical conductivity, and minimizing the carbon coating layer suppresses the phenomenon of reduced volumetric energy density. Furthermore, the excessively high carbon content is advantageous in preventing detachment from the current collector during electrode plate manufacturing.

[0057] <Method for producing olivine-based cathode active material for lithium secondary batteries> Another embodiment of the present invention provides a method for producing an olivine-based cathode active material for lithium secondary batteries, comprising the steps of: preparing a first reaction solution in which iron raw material, phosphorus raw material, and doping raw material are dissolved in water; a second reaction solution in which lithium raw material is dissolved in water; and an organic solvent in which a dispersant is dissolved; adding the first reaction solution and the second reaction solution to a reactor containing the organic solvent in which the dispersant is dissolved, while stirring, to obtain an organic solution; heating the reactor to a temperature in the range of 160°C to 180°C and performing a reflux reaction under atmospheric pressure conditions with the reactor not sealed to obtain a precipitate; and separating and drying the precipitate and then calcining it in a reducing atmosphere to obtain an olivine-based cathode active material.

[0058] The present invention provides a method for producing an olivine-based positive electrode active material for lithium secondary batteries, comprising the steps of preparing a first reaction solution in which an iron raw material, a phosphorus raw material, and a doping raw material are dissolved in water, a second reaction solution in which a lithium raw material is dissolved in water, and an organic solvent in which a dispersant is dissolved.

[0059] The first reaction solution may be a reaction solution obtained by adding an iron raw material, a phosphorus raw material, and a doping raw material to water and then stirring to dissolve them. The iron raw material may be one or more selected from FeCl2·4H2O, FeSO4·7H2O, and Fe(NO3)2·6H2O, and specifically, it may be FeSO4·7H2O.

[0060] The phosphorus raw material may be one or more selected from H3PO4, NH4H2PO4, (NH4)2HPO4, NaH2PO4, Na2HPO4, LiH2PO4, and Li2HPO4.

[0061] The doping raw material may be a raw material containing one or more selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga.

[0062] The second reaction solution may be a reaction solution obtained by adding lithium raw material to water and then stirring to dissolve it.

[0063] The lithium raw material may be LiOH, Li2CO3, or LiH2PO4, Li2HPO4, or Li3PO4, but is not limited thereto.

[0064] In the step of preparing each organic solvent in which the dispersant is dissolved, the organic solvent may be an organic solvent having a boiling point in the range of 150°C to 200°C. Specifically, it may be one or more selected from dimethyl sulfoxide (DMSO), diglyme, triglyme, and dimethylformamide (DMF), and more specifically, it may be dimethyl sulfoxide (DMSO).

[0065] The dispersant may be a polymeric dispersant, and specifically, the polymeric dispersant may be one or more selected from polyvinylphenol (PVPh), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinyl sulfonic acid, polyvinyl sulfate metal salt, polyvinyl carboxylic acid, polyvinyl carboxylate metal salt, polyvinylpyridine (PVPy), copolymers thereof, cyclodextrin, dextran, polysaccharide, or polyacrylic acid (PAA).

[0066] The mass percentage of the dispersant relative to the mass of the organic solvent may be 0.2 wt% to 2 wt%.

[0067] When a dispersant is mixed with an organic solvent in the aforementioned range, it has the advantage of efficiently producing olivine-based cathode active materials with controlled particle shape and size and improved energy density, and also has the advantage of preventing particle aggregation or the generation of by-products during the reaction process.

[0068] The present invention provides a method for producing an olivine-based positive electrode active material for lithium secondary batteries, comprising the step of adding the first reaction solution and the second reaction solution to a reactor containing an organic solvent in which the dispersant is dissolved, while stirring, to obtain an organic solution.

[0069] After adding the dispersant to the reactor containing the organic solvent, it is dissolved while stirring at room temperature, and then the reactor is heated to a temperature of 80°C, specifically, 50°C to 80°C. This is advantageous for homogenizing the coprecipitation reaction of the Li(FeMn)PO4 element in the reactor when the first and second reaction solutions, which will be described later, are added.

[0070] When heating the reactor, an inert gas can be continuously supplied to maintain an inert atmosphere inside the reactor. This is preferable because it has the advantage of preventing oxidation caused by the introduction of active components such as oxygen during the heating process, thereby preventing the generation of by-reaction products.

[0071] The first reaction solution, in which the iron raw material, phosphorus raw material, and doping raw material are dissolved in the prepared water, is added to the reactor containing the organic solvent in which the heated dispersant is dissolved, at a predetermined rate. At this time, the inside of the reactor can be continuously stirred by a separate stirring member or stirring device.

[0072] Simultaneously, a second reaction solution, in which lithium raw material is dissolved in water, is added at a predetermined rate.

[0073] At this time, the pH value of the substance inside the reactor is kept constant, specifically between 6.0 and 7.0. Maintaining the pH value within this range is preferable because it has the advantage of efficiently producing olivine-based cathode active materials with controlled particle shape and size, and improved energy density.

[0074] The ratio of the number of moles of lithium element to the total number of moles of iron element and doping element in the obtained organic solution may be 1.00 to 1.02, and more specifically, it may be 1.00 to 1.01.

[0075] When the ratio of the number of moles of lithium element to the total number of moles of iron element and doping element in the organic solution falls within the aforementioned range, it is preferable because it offers an advantage in producing an olivine-based cathode active material with fewer impurities.

[0076] The present invention provides a method for producing an olivine-based positive electrode active material for lithium secondary batteries, which includes the step of heating the reactor to maintain an internal temperature of 160°C to 180°C and carrying out the reaction under atmospheric pressure conditions without sealing the reactor to obtain a precipitate.

[0077] After the first and second reaction solutions have been added to the reactor containing the organic solvent in which the dispersant is dissolved, the reactor is heated so that the internal temperature of the substances contained in the reactor reaches 160°C to 180°C. Then, the reactor is kept at this temperature and reacted at atmospheric pressure without sealing the reactor for at least 3 hours, specifically 3 to 24 hours, to obtain a precipitate. At this time, a Deak-stark apparatus may be connected to the reactor, and a reflux condenser may be attached to it to perform a reflux step.

[0078] After the precipitate acquisition reaction is complete, the precipitate can be separated by centrifugation or filter pressing, and the separated precipitate can be washed two or more times with distilled water. Through these two or more washes, impurities such as organic solvents and dispersants remaining in the precipitate can be removed.

[0079] The washed precipitate can be dried in a drying apparatus, and an inert gas can be continuously supplied to the drying apparatus.

[0080] After the dried precipitate is charged into the furnace, it is calcined at a temperature of 550°C to 750°C for 12 hours or more while continuously supplying a reducing gas to obtain a carbon-coated olivine-based cathode active material.

[0081] In yet another embodiment of the present invention, the step of crushing the lithium iron phosphate compound may be further included, but is not limited thereto.

[0082] In yet another embodiment of the present invention, the dried precipitate can be mixed with a carbon coating raw material, milled, and then reduced and calcined to obtain a carbon-coated olivine-based cathode active material. The mass percentage of the carbon coating raw material relative to the mass of the dried precipitate may be 5 wt% to 15 wt%. Mixing the carbon coating raw material within this range is preferable because it has the advantage of being able to produce an olivine-based cathode active material with the carbon content controlled as desired in the present invention.

[0083] The carbon coating raw material may be one or more selected from cellulose, glucose, sucrose, fructose, lactose, or maltose, and is not particularly limited in type as long as it can effectively form a carbon coating layer by the method according to the present invention.

[0084] Specifically, the carbon coating raw material may be cellulose.

[0085] The carbon-coated olivine-based cathode active material obtained by the above process has been described in detail above, so it will be omitted here. [Examples]

[0086] The following describes preferred embodiments and comparative examples of the present invention. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to these embodiments.

[0087] (Manufacturing of olivine-based cathode active materials) 3.371 g of FeSO4·7H2O, 8.196 g of MnSO4·H2O, and 6.9714 g of 85% H3PO4 were added to 200 g of distilled water (H2O), and then stirred to prepare the first reaction solution.

[0088] Furthermore, 7.6297g of LiOH·H2O was added to 200g of distilled water (H2O), and then stirred to dissolve it, thereby producing a basic lithium solution, which was the second reaction solution.

[0089] After dissolving 200g of DMSO and 1g of PVP (Polyvinyl pyrrolidone, a dispersant) in a coprecipitation reactor equipped with a condenser to prepare an organic solution, argon gas is purged, and the reactor is heated while stirring the internal solution until the solution temperature reaches 80°C.

[0090] The first reaction solution is added to the heated coprecipitation reactor at a constant rate, and the second reaction solution is added while adjusting the rate of addition so that the pH is maintained at approximately 6.5.

[0091] After the first and second reaction solutions have been added, the reactor is heated until the temperature of the mixture inside the reactor reaches 160°C, and the reflux reaction is carried out while maintaining the temperature at 160°C for a predetermined time.

[0092] After the reaction is complete, the resulting precipitate is separated by centrifugation or filter pressing, washed twice with water, and then dried in a drying oven. 10 wt% cellulose is mixed with the dried powder by mass and dry-mixed in a mixer. The mixture is then placed in a 650°C furnace and calcined in a nitrogen gas atmosphere for 1 hour to produce carbon-coated LFMP, an olivine-based cathode active material for lithium secondary batteries.

[0093] The amounts of raw material substances mixed in Examples 1 to 3 and Comparative Examples 1 to 4 according to the above manufacturing method are shown in Table 1 below, and the operating conditions are shown in Table 2 below.

[0094] [Table 1]

[0095] In Table 1 above, Comparative Example 2 was mixed with DEG (diethylene glycol) instead of DMSO. Meanwhile, in Comparative Example 2, experiments were conducted maintaining reaction times of 3, 6, 9, 15, and 30 hours instead of 24 hours.

[0096] [Table 2]

[0097] (SEM analysis) Figure 1 shows the SME analysis image of LFMP produced according to Examples 1 to 3, and Figure 2 shows the SME analysis image of LFMP produced according to Comparative Examples 2 to 4.

[0098] Referring to Figure 1, it can be confirmed that the LFMPs produced according to Examples 1 to 3 were formed as single entities, consisting of rod-shaped particles with an average length of the long side in the range of 250 nm to 350 nm and an average length of the short side in the range of 70 nm to 100 nm, and flake-shaped particles with an average length of the long axis of the wide surface in the range of 350 nm to 450 nm and an average length of the short axis in the range of 200 nm to 250 nm. Furthermore, it can be confirmed that the number percentage of flake-shaped particles relative to the total number of rod-shaped and flake-shaped particles was 50% or less.

[0099] In contrast, as shown in Figure 2, the LFMP produced according to Comparative Examples 2 to 4 appeared to be composed of rod-shaped particles and flake-shaped particles aggregating to form a single particle. Furthermore, it can be confirmed that, in addition to rod-shaped and flake-shaped particles, small-particle-sized powder-like particles also appeared aggregated with the aforementioned rod-shaped and flake-shaped particles.

[0100] (XRD analysis) Figure 3 shows the XRD analysis results of LFMP produced according to Example 2 and Example 3, Figure 4 shows the XRD analysis results of LFMP produced according to Example 2 and Comparative Example 4, and Figure 5 shows the XRD analysis results of LFMP produced according to Comparative Example 2.

[0101] On the other hand, Figure 5 also shows the XRD analysis results of LFMP produced by a method that differs only from Comparative Example 2 in reflux reaction time.

[0102] Referring to Figure 3, it can be confirmed that LFMP produced according to Embodiment 2, in which the pH was maintained at 6 and the reflux reaction time was 3 hours, and Embodiment 3, in which the reflux reaction time was 3 hours, exhibit almost identical crystal structures.

[0103] Referring to Figure 4, in Comparative Example 4, where LiOH was added at a ratio of 1.03 moles of lithium to the total moles of iron and manganese, a Li3PO4 peak due to excess Li was observed, confirming the generation of impurities. In contrast, in Embodiment 4, where LiOH was added at a ratio of 1.00 moles of lithium to the total moles of iron and manganese, it was confirmed that almost no impurities were generated.

[0104] Referring to Figure 5, when DEG is used as the organic solvent instead of DMSO, XRD analysis of the reflux reaction time shows that the (Mn,Fe)5H2(PO4)4·4H2O phase was formed up to 15 hours of reaction, and after 24 hours of reaction, LIFe 0.2 Mn 0.8 It can be confirmed that the product was converted to PO4. If the reflux reaction time is less than 24 hours, it can be confirmed that impurities have been generated, and it can be confirmed that the product is switched to LFMP after 24 hours of reaction.

[0105] (Manufacturing of coin-type half-cells) After manufacturing a CR2032 coin cell using the LFP cathode active material produced according to the above examples and comparative examples, electrochemical evaluation was performed.

[0106] Specifically, a slurry for electrode plate manufacturing was produced by mixing LFP positive electrode active material: conductive material (Super P): binder (PVDF) in a mass-based ratio of 90:5:5 with NMP (N-Methyl-2-pyrrolidone) solvent to adjust the slurry viscosity.

[0107] The manufactured slurry was coated onto a 15 μm thick aluminum foil using a doctor blade, dried, and then rolled to produce a positive electrode plate. Here, the electrode loading was approximately 10 mg / cm². 2 The above is the total plate density, which is approximately 2 g / cm³. 3 That concludes my explanation.

[0108] After mixing 1M LiPF6 and EC:DMC:EMC=3:4:3 (vol%) as the electrolyte, 1.5 wt% vinylene carbonate (VC) was added. Coin-type half-cells were fabricated using a PP separation membrane and a lithium anode (200 μm, Honzo metal), and then aged at room temperature for 10 hours. The measurement voltage range was 4.3V to 2.5V, and the 1C reference capacity was evaluated using 150 mAh / g. The results are shown in Table 3 below.

[0109] [Table 3]

[0110] Referring to Table 3, it can be confirmed that the battery manufactured according to the embodiment of the present invention has superior charging and discharging capacity compared to the battery manufactured according to the comparative example.

[0111] The present invention is not limited to the embodiments described above and can be manufactured in a variety of different forms. Those with ordinary skill in the art to which the present invention pertains will understand that the invention can be implemented in other specific forms without altering the technical idea or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting.

Claims

1. Rod-shaped particles having an average length of 250 nm to 350 nm on their long sides and an average length of 70 nm to 100 nm on their short sides; and Flake-like particles having a major axis average length of 200 nm to 450 nm on the broad surface and a minor axis average length of 100 nm to 250 nm; The percentage of flake-shaped particles relative to the total number of rod-shaped and flake-shaped particles is in the range of 1% to 50%. Olivine-based cathode active material for lithium secondary batteries.

2. The ratio of the length of the long side to the length of the short side of the rod-shaped particle is in the range of 1.5 to 8.

0. The olivine-based cathode active material for lithium secondary batteries according to claim 1.

3. The aspect ratio of the broad surface of the aforementioned flake-like particles is in the range of 1.0 to 3.

0. The olivine-based positive electrode active material for lithium secondary batteries according to any one of claims 1 to 2.

4. The chemical composition of the rod-shaped particles and flake-shaped particles is represented by the following chemical formula 1: The olivine-based positive electrode active material for lithium secondary batteries according to any one of claims 1 to 3. [Chemical formula 1] Li ｘ (Fe ｙ M １－ｙ )PO ４ Here, 0.99 ≤ x ≤ 1.03, 0.2 ≤ y ≤ 0.6, and M is one or more selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga.

5. The specific surface area of ​​the olivine-based cathode active material for the lithium secondary battery is 10 m² ２ / g or 30m ２ It is within the range of / g. The olivine-based positive electrode active material for lithium secondary batteries according to any one of claims 1 to 4.

6. The olivine-based positive electrode active material for lithium secondary batteries is, It includes a carbon coating layer located on the external surface. The olivine-based positive electrode active material for lithium secondary batteries according to any one of claims 1 to 5.

7. The mass percentage of carbon relative to the total mass of the olivine-based positive electrode active material for the lithium secondary battery is in the range of 1 wt% to 2 wt%. The olivine-based positive electrode active material for lithium secondary batteries according to any one of claims 1 to 6.

8. The carbon coating layer is located in a range of 90% to 100% of the total surface area of ​​the olivine-based cathode active material for the lithium secondary battery. The olivine-based cathode active material for lithium secondary batteries according to claim 6.

9. The aforementioned rod-shaped particles have rounded ends along the length of their longer sides. The olivine-based positive electrode active material for lithium secondary batteries according to any one of claims 1 to 8.

10. The aforementioned flake-like particles have a shape in which the length of the minor axis gradually decreases from the center of the major axis toward both ends. The olivine-based positive electrode active material for lithium secondary batteries according to any one of claims 1 to 9.

11. The steps include preparing a first reaction solution in which iron raw material, phosphorus raw material, and doping raw material are dissolved in water, a second reaction solution in which lithium raw material is dissolved in water, and an organic solvent in which a dispersant is dissolved; A step of obtaining an organic solution by adding the first reaction solution and the second reaction solution to a reactor containing an organic solvent in which the dispersant is dissolved, while stirring; The steps of heating the reactor to maintain an internal temperature of 160°C to 180°C, carrying out the reaction under atmospheric pressure conditions with the reactor not sealed, to obtain a precipitate; and The steps include: separating and drying the precipitate, then calcining it in a reducing atmosphere to obtain an olivine-based cathode active material; A method for producing olivine-based cathode active material for lithium secondary batteries.

12. The step of heating the reactor to maintain an internal temperature of 160°C to 180°C and carrying out the reaction under atmospheric pressure conditions without sealing the reactor to obtain a precipitate is: This is carried out by a reflux process. A method for producing an olivine-based cathode active material for a lithium secondary battery according to claim 11.

13. In the step of preparing each organic solvent in which the dispersant is dissolved, The aforementioned organic solvent has a boiling point in the range of 150°C to 200°C. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 12.

14. In the step of preparing each organic solvent in which the dispersant is dissolved, The aforementioned organic solvent is one or more selected from dimethyl sulfoxide (DMSO), diglyme, triglyme, and dimethylformamide (DMF). A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 13.

15. In the step of preparing each organic solvent in which the dispersant is dissolved, The dispersant is one or more selected from polyvinylpyrrolidone (PVP), polyvinylphenol (PVPh), polyvinyl alcohol (PVA), polyvinyl sulfonic acid, polyvinyl sulfate metal salt, polyvinyl carboxylic acid, polyvinyl carboxylate metal salt, polyvinylpyridine (PVPy), copolymers thereof, cyclodextrin, dextran, polysaccharide, or polyacrylic acid (PAA). A method for producing an olivine-based cathode active material for a lithium secondary battery according to any one of claims 11 to 14.

16. The step of preparing an organic solvent in which the dispersant is dissolved is: A step of stirring and dissolving the organic solvent and dispersant introduced into the reactor; The step of heating the organic solvent in which the dispersant is dissolved to a temperature of 50°C to 80°C; A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 15.

17. The step of heating the organic solvent in which the dispersant is dissolved to a temperature in the range of 50°C to 80°C is: This involves continuously supplying an inert gas to the reactor and heating it. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 16.

18. In the step of preparing an organic solvent in which the dispersant is dissolved, The mass percentage of the dispersant relative to the mass of the organic solvent is 0.2 wt% to 2 wt%. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 17.

19. In the step of obtaining an organic solution by adding the first reaction solution and the second reaction solution to a reactor containing an organic solvent in which the dispersant is dissolved, while stirring, The ratio of the number of moles of lithium element to the total number of moles of iron element and doping element in the obtained organic solution is between 1.00 and 1.

02. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 18.

20. The step of obtaining an organic solution by adding the first reaction solution and the second reaction solution to a reactor containing an organic solvent in which the dispersant is dissolved, while stirring, is as follows: The first reaction solution and the second reaction solution are introduced into the reactor at predetermined rates. The objective is to maintain a constant pH value of the organic solution in the reactor. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 19.

21. The pH value of the organic solution in the reactor is between 6.0 and 7.

0. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 20.

22. The step of heating the reactor to a temperature in the range of 160°C to 180°C and performing a reflux reaction under atmospheric pressure conditions with the reactor not sealed to obtain a precipitate is: It should be done for 3 hours or 24 hours. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 21.

23. In the step of separating and drying the precipitate, and then calcining it in a reducing atmosphere to obtain an olivine-based cathode active material, The process further includes the step of separating and drying the precipitate, then mixing it with a carbon coating raw material and milling to obtain a mixture. The step involves calcining the obtained mixture in a reducing atmosphere. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 22.

24. In the step of separating and drying the precipitate, and then mixing and milling it with the carbon coating raw material to obtain a mixture, The mass percentage of the carbon coating material relative to the mass of the dried precipitate is 5 wt% to 15 wt%. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 23.

25. The step of separating and drying the precipitate, and then calcining it in a reducing atmosphere to obtain an olivine-based cathode active material, This involves firing in a reducing atmosphere at a temperature of 400°C to 700°C for at least one hour. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 24.

26. In the step of preparing a first reaction solution by dissolving the iron raw material, phosphorus raw material, and doping raw material in the aforementioned water, The doping material is a material containing one or more selected from Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, W, or Ga. A method for producing an olivine-based positive electrode active material for a lithium secondary battery according to any one of claims 11 to 25.

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